This invention pertains to dual path transmission units and, more particularly, to operating structure of or control thereof.
Dual path transmissions have been known for many years and, particularly, hydrostatic transmissions wherein two pump-motor power units are interrelated to provide a hydrostatic transmission unit and with the control of displacement of one of the power units controlling the output speed of the transmission unit as well as the direction of the output. Many different systems have been disclosed for controlling the displacement of a transmission power unit in a dual path transmission, such as the various types of mechanical linkages shown in Bowers U.S. Pat. No. 2,941,609, with the mechanical linkages going directly to the displacement control structure. The Kempson U.S. Pat. No. 3,306,385 discloses three different lever members, with one lever setting a common speed for a pair of transmission units and two additional levers providing a steer function for the transmissions.
Neither of these patents disclose control systems wherein a speed-setting control pressure is delivered directly to the displacement controls for the transmission units.
The Lauck U.S. Pat. No. Re 27,488 discloses the delivery of a control pressure signal directly to the displacement control of a hydrostatic transmission unit with a pair of master speed-steer valves for two transmissions operable by linkage with uniform operation of both valves setting a speed and differential action of the valves accomplishing a steer function.
The Chatterjea U.S. Pat. No. 3,677,362 discloses a control system wherein a first valve sets a control pressure deliverable to the displacement controls of a pair of hydrostatic transmissions and with a pair of steer valves for modifying the control pressure for steer and with all of the valves being operable by a single control lever.
The Krusche U.S. Pat. No. 3,672,161 discloses a plurality of valves each of which apparently has a speed-steer function and with a universally movable lever positioned for operation of different groupings of such valves.
None of the foregoing patents disclose a system having a speed valve for setting a common control pressure for a pair of hydrostatic transmissions and a pair of steer valves with an actuator system having a control lever at a convenient location, remote from the valves and with a plurality of motion-transmitting linkages extended therebetween for imparting either independent or conjoint operation of the ratio valve and the steer valves.